zfs discuss - Aug 2010 - When is the L2ARC refreshed if on a separate drive?

I''m running a mirrored pair of 2 TB SATA drives as my data storage
drives on my home workstation, a Core i7-based machine with 10 GB of RAM. I
recently added a sandforce-based 60 GB SSD (OCZ Vertex 2, NOT the pro version)
as an L2ARC to the single mirrored pair. I''m running B134, with ZFS
pool version 22, with dedup enabled. If I understand correctly, the dedup table
should be in the L2ARC on the SSD, and I should have enough RAM to keep the
references to that table in memory, and that this is therefore a well-performing
solution.

My question is what happens at power off. Does the cache device essentially get
cleared, and the machine has to rebuild it when it boots? Or is it persistent.
That is, should performance improve after a little while following a reboot, or
is it always constant once it builds the L2ARC once?

Rather informally, it sometimes seems that the hard drives are a bit slower the
first time they load a program now, vs. when I didn''t have the SSD
installed as a cache device on the pool. But this is mainly an impression.
Thanks for your help!
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On 03 August, 2010 - valrhona at gmail.com sent me these 1,2K bytes:
> I''m running a mirrored pair of 2 TB SATA drives as my data storage
drives on my home workstation, a Core i7-based machine with 10 GB of RAM. I
recently added a sandforce-based 60 GB SSD (OCZ Vertex 2, NOT the pro version)
as an L2ARC to the single mirrored pair. I''m running B134, with ZFS
pool version 22, with dedup enabled. If I understand correctly, the dedup table
should be in the L2ARC on the SSD, and I should have enough RAM to keep the
references to that table in memory, and that this is therefore a well-performing
solution.
> 
> My question is what happens at power off. Does the cache device essentially
get cleared, and the machine has to rebuild it when it boots? Or is it
persistent. That is, should performance improve after a little while following a
reboot, or is it always constant once it builds the L2ARC once?
L2ARC is currently cleared at boot. There is an RFE to make it
persistent.

/Tomas
-- 
Tomas ?gren, stric at acc.umu.se, http://www.acc.umu.se/~stric/
|- Student at Computing Science, University of Ume?
`- Sysadmin at {cs,acc}.umu.se

Thanks for the info!
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